Perforating blade

ABSTRACT

Perforating blades for perforating traveling webs of material such as paper in high speed apparatus are made from cold rolled steel which is hardened in a vacuum furnace to produce a scale free surface. The height to which the blades are ground is determined by measuring the average thickness of the blade and grinding the height of the blade to a dimension and tolerance in accordance with an equation which relates blade height to blade thickness. Thus the thickness of each blade can vary. With conventional knife rolls in which the blades form an angle of 45° relative to a radial line of the knife roll, the sum of the height and thickness for each blade in the knife roll is equal.

CROSS REFERENCE TO RELATED APPLICATION

This appliation is a divisional application of Ser. No. 512,839 filedOct. 4, 1974, now U.S. Pat. No. 3,975,452. U.S. Pat. No. 3,973,452 is acontinuation-in-part application of Ser. No. 317,838 filed Dec. 22,1972, and now abandoned.

BACKGROUND OF INVENTION

The invention relates to perforating blades used in high speed webcutting apparatus for the transverse perforating of a web such as theapparatus described in U.S. Pat. No. 2,870,840. Prior art perforatingblades such as those disclosed in U.S. Pat. No. 3,190,163 areconstructed of standard sheet steel stock, and the blades are ground tocertain thicknesses and heights within specified tolerances to providethe desired blade extension. The grinding of the thickness of large flatsurfaces of the blades to meet the customer's specifications andtolerances results in considerable expense in manufacturing the blades.The blades are typically ground to one of three thicknesses: 0.032;0.040; and 0.047. The following blade heights are in common usage withinthe industry: 0.875; 0.906; 0.925; and 1.000. Operators of thisperforating apparatus standardize on a height for their particularequipment (for instance 0.875) and then vary the thickness between thethree commonly available sizes according to the individual preference ofthe operator of this perforating apparatus.

SUMMARY OF INVENTION

The invention provides a new perforating blade and a method of makingthe blade in which surface grinding of the large flat surfaces is notrequired. The invention recognizes the relationship between height andthickness of the blade, both of which contribute to the total bladeextension of the perforating blades from the knife roll towards thecooperating anvil. This is because the perforating blades are inclinedwith respect to a radial line drawn from their farthest radial extensionto the knife roll center.

In practice of the method, hardened cold rolled high speed steel is usedfor the blade blanks. The blades are hardened in a vacuum furnace toproduce a scale free surface. After the blades are hardened, the averagethickness of the blade is measured over the surface. The blade height isthen ground to a height and with a tolerance according to an equationwhich relates blade height to blade thickness.

Inasmuch as the blade is not surface ground on the large flat sides, thesteel can be purchased in a thinner gauge than the steel used to makeblades according to the prior art process. In addition, the blade sidesof blades made in accordance with the invention have a much smootherfinish of for instance six microinches RMS and therefore are much lesslikely to break when stressed, because there are minimal surface cracksfor stress concentrations to develop. The elimination of surfacegrinding substantially reduces the cost of the blades. In addition,blades made in accordance with the invention should have a longer lifebecause less surface stresses are induced on the blade cutting edge bythe elimination of grinding one of the two surfaces which makes up thecutting surface.

With conventional knife rolls as shown in the aforementioned patents,the blades form an angle of 45° with a radial line from the knife rollcenter. This simplifies the equation, relating height to width, and thesum of the height and width for each blade in the knife roll will beapproximately equal, although the thickness and height of each blade mayvary considerably. However, the projection of all blades from the kniferoll will be substantially equal.

Further objects, advantages and features of the invention will becomeapparent from the following disclosure.

DRAWINGS

FIG. 1 is a fragmentary diagrammatic end view of a knife roll,perforating blade and cooperating anvil in web perforating apparatus.

FIG. 2 is a side view of the parts shown in FIG. 1.

FIG. 3 is a diagrammatic sectional view showing engagement of theperforating blade and the anvil.

FIG. 4 is an enlarged view of the perforating blade shown in FIG. 3.

FIG. 5 is a fragmentary and diagrammatic enlarged view of a knife rollwith three perforating blades of different thicknesses mounted in thesame slot.

FIG. 6 is an enlarged diagrammatic end view of a knife roll andperforating blades.

DESCRIPTION OF PREFERRED EMBODIMENT

Although the disclosure hereof is detailed and exact to enable thoseskilled in the art to practice the invention, the physical embodimentsherein disclosed merely exemplify the invention which may be embodied inother specific structure. The scope of the invention is defined in theclaims appended hereto.

For purposes of exemplification, one type of paper perforating blade isshown and described in a specific type of perforating apparatus. Othertypes of perforating blades with different sizes than described hereinare within the purview of the invention.

In the drawings, FIGS. 1 and 6 show a knife roll 10 on which a pluralityof perforating blades 12 are installed. The knife roll is typically 12inches in diameter and eight feet long. The perforating blades 12 areabout 41/2 inches long by one inch high and 1/32 inch thick. The blades12 have four cutting edges 16, 18, 20 and 22. The cutting edges are inthe form of a series of lands 24 separated by notches or gaps 26.

In FIG. 6, an end view of the complete knife roll 10 is illustrated.This knife roll has five perforating blades 12 arranged around theperiphery. Each blade is sitting in a recess 13 machined in the kniferoll, each recess of which is so machined that the distance dr from thebottom of the recess to the center of the knife roll is the same, andthat the angle φ which the side of the recess makes with a lineperpendicular to the knife roll face is the same for all recesses.

The perforating blades 12 are secured to the knife roll 10 by clamps 30and clamp bolts 32. The perforating blade cooperates with an anvil 36which is diagrammatically shown in the drawings without an anvil clamp.The anvil 36 does not move during machine operation. The paper web 40 isarranged around the knife roll 10 and the knife roll rotates at the samesurface speed as the web 40. There is no relative motion between the weband the knife roll surface.

Perforations in the web 40 are effected when the rotating perforatingblade 12 with the web 40 arranged over the blade comes in contact withthe anvil 36. The perforating blade 12 projects a sufficient distancefrom the knife roll 10 so that it strikes the edge 37 of the anvil 36.For the perforating blade 12 to rotate past the anvil 36, the blade 12must bend, which it is designed to do, without breaking. FIG. 5illustrates the interference I. During the bending operation, the blade12 exerts enough pressure on the web squeezed between it and the anvil36 that a cut, or perforation is effected. As thus far described, theapparatus is conventional perforating apparatus.

The perforating blades of the invention are made from cold-rolled,annealed, high speed steel. This material can be manufactured with atotal thickness variation, in the range of 0.032 inches to 0.050 inches,of typically 0.004 inches. Furthermore, over an area of l inch high by41/2 inches long, the steel sides will be parallel to within 0.001 inch.

The material for the perforating blades of the invention is obtained inthe fully annealed form, and in blanks slightly oversized on the lengthand height dimensions. The thickness of the blanks as obtained is asclose to finished thickness as can be rolled by the steel mill. Notethat even though the thickness from blade to blade may vary as much as0.004 inch in a given lot, within any given blade the thickness willvary by no more than 0.001 inch. This is a direct result of theparallelity requirement discussed above.

The blade blanks are hardened in a vacuum furnace. Because this steel is"cold-rolled" to produce the finished "as-rolled" thickness, nodecarburization is produced on the steel surface of the mill. As aresult, the steel can be hardened without first removing anydecarburized surface, as is necessary in steel finished by "hot-rolling"techniques. Furthermore, since the hardening operation is performed in avacuum, no scale develops on the surface. The material, therefore, doesnot have to be ground on the thickness dimension, if the purpose of suchgrinding is solely to remove heat-treating scale. Although a majoradvantage of the invention is to eliminate or reduce surface grinding,some of the further advantages of the invention can be obtained if theheight is ground as subsequently described after some surface grinding.

The typical Δt_(d) variation in the blade thickness as hardened is 0.004inch, which if combined with a typical Δh_(d) variation of height of0.001 inch, would lead to large variations in the radial extension ofthe blade from the knife roll. Variations of this type are unacceptableto most practitioners of the art of operating perforating machinery.

I have discovered the relationship of thickness and height with respectto total blade extension. FIG. 4 shows how both the thickness t_(d) andheight h_(d) effect the projection of the blade 12 toward the anvil.Prior to grinding the height of a blade, I measure the thickness of eachblade in several places and grind its height h to a value given by thefollowing equation:

    h = (h.sub.d + Δ h.sub.d /2) + (t.sub.d + Δt.sub.d /2) cot θ - t cot θ ;

and in which:

t_(d) .tbd. the minimum predetermined thickness of a blade,

t_(d) + Δt_(d) .tbd. the maximum predetermined thickness of a blade,

Δt_(d) .tbd. the maximum predetermined thickness variation,

h_(d) .tbd. the minimum predetermined height,

h_(d) + Δh_(d) .tbd. the maximum predetermined height,

Δh_(d) .tbd. the maximum predetermined height variation.

θ .tbd. the angle the blade height side makes with a plane Pperpendicular to the radial line R from the farthest radial extension ofthe blade to the center of the knife roll, when the blade is at itsminimum predetermined height and thickness,

t .tbd. the average thickness of the blade as measured,

and in which the variation in thickness for this blade, which is definedas Δt = t_(max) - t_(min), satisfies the following relationship: Δt <Δt_(d) + Δ h_(d) tan θ, where

t_(min) .tbd. the minimum thickness of the blade as measured,

t_(max) .tbd. the maximum thickness of the blade as measured.

I prefer for simplicity to determine t from

    t = 0.5(t.sub.min + t.sub.max).

Note that more complicated methods are avialable for determining theaverage thickness.

The allowable plus or minus deviation of the blade height as ground forthe blade 12 is calculated from

    Δh = 1/2(Δh.sub.d + Δt.sub.d cot θ - Δt cot θ )

where Δh is the allowable plus or minus deivation in the blade heightfrom the height h for the blade.

As an example in the use of these equations in my invention, a customerwould specify the following information on the type of blades he isusing:

t_(d) = 0.040, the minimum predetermined blade thickness,

t_(d) + Δ t_(d) = 0..042, the maximum predetermined blade thickness,

h_(d) = 0.8745, the minimum predetermined blade height,

h_(d) + Δh_(d) = 0.8755, the maximum predetermined blade height,

θ = 45°, the blade angle.

To satisfy this customer's requirement, I would pick a blade whosethickness is close to that required by the customer. As an example, onthe blade I chose, I would measure the following:

t_(max) = 0.0398

t_(min) = 0.0390

Using these values in the above equations, I calculate

    h = 0.8766,

which is the height to which I grind the blade. The allowable plus orminus deviation of this height from the value of 0.8756 is calculated tobe Δh = 0.0011 which Δh is the plus or minus variation I allow for theblade I am manufacturing.

After the height is ground, the notches 26 can be formed. The method ofthe invention can also be employed to make perforating blades having aradius as shown in U.S. Pat. No. 3,190,163. the height h to which theblade will be ground is the height of the blade at the ends of theblade, for instance, at 21 in FIG. 7. After the blade is ground toheight H, and the notches formed, the radius is machined.

In FIG. 5 is illustrated one perforating blade recess with threedifferent blades 51, 52, 53 schematically mounted in it. These bladesall have the same radial projection distance R_(p) from the knife rollcenter KC, yet none of them have the same thickness or height. However,all of the blades have the same sum of their thickness and height.Mathematically this would be expressed as:

    h.sub.1 + t.sub.1 = h.sub.2 + t.sub.2 = h .sub.3 + t.sub.3 =  constant (1)

The above relationship is mathematically quite simple where the angle φin FIGS. 5 and 6 is 45°, as is common in the industry. If this anglewere something other than 45°, the height and thickness of any twoperforating blades would have to solve the following equation:

    h.sub.1 cos φ + t.sub.1 sinφ = h.sub.2 cosφ + t.sub.2 sinφ = constant                                                (2)

The equations 1 are 2 are derived from the previous equation h = (h_(d)= Δh_(d) /2) + (t_(d) + Δ t_(d) /2) - t cot θ as follows:

Place the last term on the right into the left side to obtain h + t cotθ = (h_(d) - Δh_(d) /2) + (t_(d) + Δt_(d) /2).

Everything on the right side of the equation just above ispredetermined, not variable, and therefore a constant.

Define this constant to be C₁. The above equation now becomes

    h + t cot θ = C.sub.1

however, cot θ = cos θ/sin θ. Substituting this in the above equation,and multiplying through by sin θ we arrive at

    h sin θ + t cos θ = C.sub.1 sin θ

Since θ is the same for all blades in a knife roll, C₁ sin θ is simply anew constant which we will denote by C. We have therefore

    h sin θ + t cos θ = C

since θ = 90° - φ

sin θ = sin (90° - φ) = cos φ

and

    cos θ = cos (90° - φ) = sin φ

we have

    h cos φ + t sin φ = C

this equation sets forth that the blade height and thickness for anyblade in the knife roll must satisfy the above relationship. If wedenote the first blade by subscript 1, the second by subscript 2, and soon, we have

    h.sub.1 sin φ + t.sub.1 cos φ = h.sub.2 sin φ + t.sub.2 cos φ = C

in the above equation, if φ is set equal to 45°, we can then divide outthe sin 45° and cos 45° term, since they are equal to each other. Wethen get for the case of φ = 45°, h₁ + t₁ = h₂ + t₂ = C₂, where C₂ isanother constant.

The realtionship of h₁ + t₁ = h₂ + t₂ = C₂ is useful because now steelcan be purchased for perforating blades in a thickness nominally equalto that specified by the operator of this apparatus. Furthermore, if thesteel is scale free, as cold-rolled high speed steel is, it can behardened in a vacuum furnace without any surface preparation. Likewise,the hardening operation produces no scale on the surface of theperforating blade. Therefore, the steel can be purchased in the nominalgauge needed by the finished product, and furthermore, no surfacefinishing need be performed on these blades.

However, the thickness of the steel as obtained from the steel produceris not identically the same from piece to piece. But by using the factthat the sum of the height and thickness is a constant, I am able toadjust the height to compensate for the variation in thickness in such amanner as to keep the projection distance constant for all bladesmounted in a knife roll.

Although the thickness of blades in a prior art knife roll will varywithin a tolerance range of ± 0.00025 to ± 0.001 inches, blades producedin accordance with the method of the invention can be used in the sameknife roll even though the thickness variation between individual bladesexceeds 0.002 inches as long as the projection distance is equal.

I claim:
 1. In a knife roll for use in web perforating apparatus, saidknife roll including at least two recesses for mounting perforatingblades around its periphery, said recesses having surfaces for mountingperforating blades at a common angle greater than 0° but less than 90°with a radial line, and wherein said recesses are formed fromintersecting surfaces on the knife roll with the intersections of saidrecesses being at a common distance from the axis of said roll, theimprovement comprising a plurality of perforating blades loaded in saidknife roll recesses, at least one of said blades having a differentthickness than the remainder of said blades and in which all bladesproject from said knife roll face a common distance.
 2. The improvementof claim 1 wherein the sides of said blades are in the as-rolled andhardened condition.
 3. A knife roll in accordance with claim 1 whereinsaid one blade having a different thickness than the remainder of theblades has a thickness difference from at least one of said remainder ofblades in excess of 0.002 inches.
 4. A knife roll for web perforatingapparatus including a plurality of perforating blades pojecting at anangle of 45° with respect to a radial line through the axis of saidknife roll and in which the thickness and height of each of said bladesvaries but in which the sum of the thickness and height for each bladeis substantially equal, thereby causing each of said blades to project acommon distance from siad knife roll.